One-pot construction of nitrogen-rich polymeric ionic porous networks for effective CO2 capture and fixation

Facile preparation of ionic porous networks (IPNs) with large and permanent porosity is highly desirable for CO2 capture and transformation but remains a challenge. Here we report a one-pot base-mediated construction of nitrogen-rich IPNs through a combination of nucleophilic substitution and quaternisation chemistry from H-imidazole. This strategy, as proven by the model reactions of 1H-imidazole or 1-methyl-1H-imidazole with cyanuric chloride, allows for fine regulation of porosity and physicochemical properties, leading to nitrogen-rich IPNs featuring abundant ionic units and radicals. The as-prepared networks, termed IPN-CSUs, efficiently capture CO2 (80.1 cc g−1 at 273 K/1 bar) with an ideal CO2/N2 selectivity of 139.7. They can also effectively catalyse the cycloaddition reaction between CO2 and epoxides with high yields of up to 99% under mild conditions (0.1 MPa, 298 K), suggesting their possible applications in the fields of both selective molecular separation and conversion. Unlike the previously known strategies generally involving single coupling chemistry, our strategy combining two coupling routes in one pot appears to be unique and potentially applicable to other building blocks.

CO2 capacity and catalytic performance for model products Figure S11 NMR analysis for crude products from catalytic experiments Section S1. Materials Cyanuric chloride, and 1H-imidazole were purchased from Alfa Aesar Chemical Inc. and used as received without further purification. 1-Methyl-2-pyrrolidinone dichloromethane, acetone, tetrahydrofuran and chloroform were purified by distillation after removal of water over CaH2 and stored with 4 Å molecular sieves prior to use.
Unless other stated, all other solvents or regents used were commercially available and used without further purification.

Section S2. Instruments and methods
Using selected solvent mediums, hydrogen nuclear magnetic resonance ( 1 H NMR) and carbon nuclear magnetic resonance ( 13 C NMR) spectroscopic measurements of the soluble samples were recorded on a Bruker AV-400 spectrometer with tetramethylsilane (TMS) as the internal reference. Solid-state 13 C cross polarization magic angle spinning ( 13 C CP/MAS) NMR spectra were obtained on a Bruker Avance III 400 NMR spectrometer. The spectra were obtained by using a contact time of 2.0 ms and a relaxation delay of 10.0 s. Using KBr disks, Fourier transform infrared spectroscopy (FT-IR) spectra of the powdered samples was collected in a transmission mode on a VARIAN 1000 FT-IR (scimitar series) spectrometer. Elemental analysis including carbon, hydrogen, and nitrogen was collected on a FlashEA 2000 Elemental Analyzer using a CHN model. Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDS) experiments were performed on a FEI Quanta-200 scanning electron microscope. For Transmission electron microscopy (TEM) measurements, samples were coated with a thin film of platinum. It was carried out on a JEOL JEM 3010 at 300 kV. Powder X-ray Diffraction (PXRD) pattern of the samples was collected on a Bruker AXS D8 Discover multi-purpose high power X-ray diffractometer. Thermogravimetric analysis (TGA) was performed using a PERKIN ELMER TGA7 instrument, and the samples was investigated from 25 o C to 800 o C at a heating rate of 10 K· min -1 under N2 atmosphere. The nitrogen adsorption and desorption isotherms were obtained by using ASAP 2020 volumetric adsorption analyzer at 77 K, and the surface area and pore size distribution of the sample were obtained using Bruner-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) models. The sample was degassed at 80 o C for 9 h under vacuum (5*10 -4 Pa) before the analysis. The cumulative apparent surface area for N2 was calculated by using the BET model range from 0.025 to 0.10 bar for the sample. The pore size distribution of sample was calculated from the adsorption branches of the isotherms according to the Nonlocal Density Functional Theory (NLDFT) method by using a carbon slit pore model. The low-pressure nitrogen adsorption and desorption isotherms were measured at 273K.
The adsorption and desorption isotherms of carbon dioxide (CO2) were obtained from the ASAP 2020 volumetric adsorption analyzer at 273 K and 298 K up to 1 bar. Isosteric heat of adsorption (QST) value of the samples towards nitrogen or CO2 was calculated by using Clausius-Clapeyron equation on the data master offline data reduction software (Micrometrics). For the catalytic cycloaddition of CO2 and epoxides, the reaction mixture after centrifugation to remove the IPN-CSUs catalyst was analysed by 1 H NMR spectroscopy to calculate the reaction yield.

Section S3. AEC measurements of model products and IPNs
The anion exchange capacity (AEC, chloride form) of model reaction products: Model C1 (0.3 g) were dissolved in concentrated nitric acid and then 0.1M silver nitrate solution in water was added drowse to the clear solution. Finally, silver chloride as precipitate was isolated and washed by acetone, and dried under vacuum till constant weight. Yield: 0.15 g, corresponding to an AEC value of 3.4 mmol g-1.
AEC of IPF-CSUs: Typically, IPF-CSU-22 (0.3 g) was dissolved in concentrated nitric acid and the undissolved substance was filtered off to obtain a clear mixture solution.
Secondly, 0.1M aqueous silver nitrate solution was added dropwise to the clear mixture solution in the condition of potassium chromate as indicator. Then, silver chloride as precipitate was isolated and washed by acetone, and finally dried under vacuum till constant weight.

Section S4. Determination for isosteric heat of adsorption
The adsorption enthalpies of these porous materials on CO2 molecules were calculated by the adsorption isotherms at different temperatures (such as 273K and 298K) to study the binding ability of IPN-CSU adsorbent molecules to small gas molecules.It is clear that physical adsorption and chemical adsorption can be defined by the size of adsorption enthalpy. Combining the CO2 adsorption isotherms at 273K and 298K, the Clausius-Claperyron equation is fitted to calculate the adsorption enthalpy. The equation is as follows: Qst is the adsorption enthalpy of CO2 by the porous body, R is the gas constant, and P1 and P2 are the corresponding CO2 adsorption capacity at T1=273K and T2=298K respectively.

Section S4. Catalytic conversion of CO2 to cyclic carbonates
Catalytic procedures: A 3-neck round bottom flask was charged with IPN-CSUs catalyst (0.098 mmol), the epoxide 2-methyloxirane (12.5 mmol) with or without TBAB catalyst (1.44 mmol). Then, CO2 (0.1 Mpa) was poured into the reactor as a reactant. The reaction mixture was stirred at 25 o C for 48 h, after which the remaining CO2 was slowly evaporated. After centrifugation to remove the catalyst, the reaction mixture was analyzed by 1 H NMR spectroscopy to determine the reaction yield.

Section S4 Figures and tables
Scheme S1 Synthetic route of Model C1.
Scheme S2 Synthetic route of Model C2 and Model C3.